Part 140

=Names=, of people, 20

=Nature=, protecting eyes, ways of, 38

=Navigating= on bottom of sea, 283

=Negative= in photography, 23

=Nerves=, sensory, receive impression, 93 transmitting impression, 22

=News=, how did the word originate? 312

=Nightmare=, cause of, 367

=Nitrogen=, what it is, 350

=Ocean=, why is it blue? 219 what makes it green? 219 why don’t water sink in? 219 where did all the water in, come from? 218 where is water at low tide, 219

=Of= what use is my hair? 143

=Of= what use are pains and aches? 410

=Oil baths=, for gun (illus.), 57

=Oil cake=, from linseed, 228

=Oil=, palm olive, in soap, 411

=Omniscope=, of submarine boat, 271

=Onions=, make tears, 38 bad effect of on eyes, 38

=Operatives=, in powder factory, girls as, 49

=Optical instruments=, based on refraction, 38

=Organic matter=, what it is, 174

=Origin of cement=, 95 of counting in tens, 19 names of people, 20 of nodding to indicate yes, 19 of shaking head to indicate no, 19 of turnpike, 104

=Oxide of zinc smelter= (illus.), 227 how obtained, 226

=Oxygen=, what it is, 349 in air, 37

=Pain=, of what use is, 410 what it is, 244

=Paint=, care of, story in, 224 how mixed, 228 uses of, 224 what used for, 224

=Paint manufacturing=, colors, what makes different, 229 buckles before corrosion (illus.), 225 buckles after corrosion (illus.), 225 buckles placed in stacks (illus.), 225 buckles taken from stacks (illus.), 225 first step in making (illus.), 224 lead buckles making (illus.), 224 lead, white, how made, 224-225 lead white used in, 224 grinding lead in oil (illus.), 228 washing the lead (illus.), 226 mixing, 228 where paints are mixed (illus.), 228 linseed oil, where obtained, 227 pressing oil from flaxseed (illus.), 228 removing oil cake from press, 228 sulphur roasting furnace (illus.), 226 zinc smelter (illus.), 227 oxide of zinc, how made, 226

=Paper=, earliest forms of, 14 sensitive in photography, 23 shells, inspection of (illus), 49 papyrus, the first, 14

=Papyrus=, invention of, 14

=Patents=, of original telephone, 73